Radio receiver



Nov. 11, 1941. E. F. ANDREWS RADIO RECEIVER Filed July 18, 1958 4Sheets-Sheet l iv m. a

III l e 5 I QWA; w Jifarzgg Nov. 11, 1941. ANDREWS 2,262,218

RADIO RECEIVER Filed July 18, 1938 4 Sheets-Sheet 2 MJWA, WZQ? Nov. 11,1941. E. F. ANDREWS 2,252,213

RADIO RECEIVER Filed July 18, 1938 4 Sheets-Sheet 5 I62 I73 I76 I74 177Mora? HMC idea 22.-

Nov. 11, 1941. ANDREWS 2,262,218

RADIO RECEIVER :5 Filed July 18, 1938 4 Sheets-Sheet 4 Patented Nov. 11, 1941 UNITED STATES PATENT OFFICE RADIO RECEIVER Edward F. Andrews,Chicago, Ill. Application July 18, 1938, Serial No. 219,713

- without taking his hand from the wheel, while 20 Claims.

This invention relates to devices for tuning radio receivers in whichtuning is effected by power means adapted to be set in operation bymanually actuated means and adapted automatically to be renderedinoperative when the receiver has been tuned to the carrier wave of abroadcasting station received with sufllcient strength. I call thisgeneral type of station selection stop-oncarrier tuning. The manuallyactuated means suitably comprises means controlling the change of anelectric current or voltage and may be located at a point remote fromthe receiver. For example, it may be a manually actuated switch which ispreferably located in remote relation to the receiver, being connectedthereto by means of a cable.

The invention also relates to means for securing the proper timing andfor equalizing and narrowing the electrical impulses which causeautomatic stoppage on the carrier to effect more exact and uniformtuning.

The invention is very advantageous for tuning all varieties of radioreceiver. It facilitates remote control and provides simple automatictuning which does not require manual adjustments for setting uppre-selected stations.

The invention is very advantageous for effecting automatic tuning forautomobile or other portable radio receivers where the receiver may bemoved out of the vicinity of certain broadcasting stations and into thevicinity of others. As the form of automatic tuning of this inventionwill tune in the stations whose carrier waves are of sufllcient strengthto cause stoppage of the power means driving the tuning element, it isnot necessary to re-set the device to tune in a new set of stations whenthe geographical location of the receiver is changed. The deviceautomatically tunes in the stations broadcasting carrier waves ofsuflicient strength, regardless of what particular stations they may be,within the tuning range of the receiver.

As tuning from one station to another is effected merely by pressing abutton, the tuning operation may be performed by the driver of anautomobile without taking his eyes from the road. He may simply continueto operate the tuning button until he hears the desired station. Thisgreatly enhances the safety of radio receiver operation by the driver ofan automobile. As only a button or switch connected to the receiver bytwo small flexible wires is required for performing the tuningoperation, this can be very conveniently mounted directly on thesteering column, where the driver may operate it the receiver may bemounted at any other suitable location in the automobile.

The invention is, of course, also adapted to the automatic tuning ofstationary or home types of receiver, and also may be remotely operatedin other ways. Also, many of the features described in connection withautomobile sets are similarly advantageous for home receivers.

The invention will readily be understood from the following descriptionof preferred embodiments thereof, taken in conjunction with theaccompanying drawings, in which:

Fig. 1 is a wiring diagram of a radio receiver embodying my invention.

Fig. 2 is a graphical illustration of tuning curves illustratingvoltages obtained in certain circuits of the receiver in Fig. 1, shownplotted against frequency.

Fig. 3 is a partial wiring diagram illustrating tuning control meansadapted to start the rotation of the condensers in either of twodirections, and showing a modification of part of the circuit shown inFig. 1.

Fig. 4 is a modification of the arrangement of Fig. 1, in which themotor circuit is opened by the relay spring.

Fig. 5 is a further modification of this invention Employing verypowerful automatic gain conrol.

Fig. 6 is a partial wiring diagram of an alternating current radioreceiver embodying a combination of features of Figs. 1 and 5.

Referring to Fig. 1, the receiver shown is a superheterodyne receiver.Specifically, it represents the Philco superheterodyne receiver builtexpressly for the 1938 Ford automobile. It will be understood that thisreceiver is shown by way of example only, since the present inventionmay be applied to any superheterodyne or to any other radio receiver.

The receiver comprises an antenna ID, a radio frequency amplifying tubeII, which is a No. 78 tube; a first detector and oscillator tube l2,which is a No. 6A7 tube; an intermediate frequency tube l3, which is aNo. 78 tube; a diode detector and first audio tube H, which is a No.tube; a power tube H, which is a No. 42 tube; a speaker l6; and a "78"power supply, designated by the reference numeral 11, which includes arectifying tube ll, which may be a No. 84 tube. Energy is supplied tothe set from the battery it, being controlled by a switch 20, which isphysically connected to the volume control 2|. The set includestransformers and other radio devices of conventional nature which needno particular description. The set is tuned by a gang 3! of threecondensers which serve to tune the antenna circuit, the grid circuit ofthe first detector i2, and the oscillator circuit. The rotors of thecondensers are mounted on a shaft 23 which rigidly carries a gear 21.The gear 24 is driven by a. worm 23 mounted on a shaft 23, which maybeprovided. with a knob 21 for manual tuninc. r

To provide for the mechanical drive of the condensers, I rigidly mounton the shaft 26 a gear 23, which gear meshes with a pinion 23 which iscarried by a short shaft 30. The shaft 30 carries projecting clutchelements 3| which are adapted to be engaged by corresponding clutchelements 32 on the shaft 33 of a reversible motor 34. The armature ofthe motor 34 is biased away from the shaft 34. This may suitably be doneby brushes 34' which bear'resiliently against the armature. When themotor 34 is energized, the flux moves the armature against the tensionof the brushes 34' so that its clutch elements 32 are moved into thepath of the clutch elements 3|. Immediately the motor is de-energized,the brushes 34- move the clutch elements 32 out of the path of theclutch elements 3| so that the inertia of the armature does not tend tomake the condenser overrun. In this way, the tendency of the condenserto overrun is substantially limited to the inertia of the condenserrotor and the drive means connected therewith.

While any type of reversible motor 34 may be employed, in the embodimentshown I employ a direct current reversible motor having two windings 35and 34, both of which are connected by a lead 31 to the battery lead 33.This connection is located on the side of the switch 20 remote from thebattery I9. I prefer to connect a grounded condenser 33 to the lead 31to attenuate high frequency disturbances. The other ends of the windings35 and 36 are connected by means of conductors 40 and 4! respectively toa single pole, double throw snap switch 42. This switch is alsoconnected by a conductor 43 to a contact 44 of a relay 45. The snapswitch 42 serves to connect the conductor 43 to one or the other of thewindings 38 and 36 so as to cause one or the other of these windings tobe energized to rotate the motorin one direction or in the oppositedirection. The switch 42 is adapted to be thrown in one direction or theother by means of pins 48 and 41. Thus, when the switch 43 is in theposition shown in Fig. 1, the winding 35 willbe energized so as to causethe motor to drive in the direction corresponding to the arrow shown onthe gear 24. When the motor has thereby moved the condensers almost totheir extreme position, the pin 46 engages the switch 42 and snaps it soas to connect the conductor 43 to the winding 36. Consequently, thedirection of rotation of the motor 34 is reversed and the drive willoccur continuously or intermittently, as will hereinafter be more fullyexplained, until the pin 41 throws the switch 42 back into the positionin which it is shown in Fig. 1, again reversing the direction ofrotation of the motor. It may here be noted that the movements of thecondenser are interrupted when the set is tuned to stations ofpredetermined strength and are resumed by manual actuation. The movementof the condensers occurs, however, in progressive steps until theyarrive at an extreme pomtion, whereupon the direction of rotation of themotor is reversed and the successive step-by-step movements of thecondensers are executed in the opposite direction.

The armature 48 of the relay 4! is adapted to engage the contact 44 andalso the contacts 49 and 53 when it is in the position shown in Fig. i.

'It is biased to this position by a'spring 5!. When the relay 45 isenergized to a sufilcient degree, the armature 43 is withdrawn from thecontacts 45, 4!, and Ill. The armature 48 is grounded and the contact 44is connected through a resistor 52 and condenser 53 to ground to preventarcing and sticking at the contact 44.

The winding of the relay 45 isconnected to one of the plates 54 of atube 55, which is a 6F8-G, having two cathodes 53 and 51, a plate IIwhich is associated with the'cathode 56, a grid II which cooperates withthe cathode 56, and another grid 80 which cooperates with the cathode I1and plate 54. This tube is employed as a diode-triode tube, the plate 33being connected to the cathode 56 which is connected through a condenser61 to ground. The grid 43 is by-passed through a condenser 33 togroundand is connected through a resistor 63 to the cathode 53. The cathode 53and the resistor 63 are connected through a resistor 84 to the contactII. The contact 53 and the resistor 84 are connected through a resistor33 to a resistor 66, which is connected to the cathode of the tube 15.The cathode of the tube I5 and the resistor 86 are connected to aconductor $1. The other end of the resistor 66, that is, the end whichis connected to the resistor 35, is connected to a re sistor 63, whichis grounded. The cathode 5'! is connected to a conductor 39.

The conductors 61 and 63 pass through a cable II which may be of anysuitable length to provide a suitable location for one or more operatingswitches 'H These switches are normally closed and they are effective sothat when either of them is opened, the motor 34 is started and itcontinues to operate as long as the switch or ceivers in the home, andthe cable 14 may be of any desired length so that the radio listener mayoccupy any position and still have complete control of the timing of thereceiver.

A transformer 12, located between the intermediate frequency tube l3 andthe diode detector and first audio tube i4 comprises, the usual windings13 and 14 in close-coupled relationship, and an additional winding II inrelatively loose-coupled relation thereto. One end of the winding I! isconnected to the grid 53. The other end I of the winding 15 is connectedto one end of the winding 14, that is, the end which is remote from theend which is connected to the two diode plates of the tube II. Thewinding II. is tuned by an adjustable fixed condenser 16 to theintermediate frequency.

The resistors 11 and 13 are ccnnectedby a conductor I3 to the grids ofthe tubes 1 i and 12 so as to apply a negative voltage thereto toautomaticaliy control the volume. Resistors 73 and ll" may be includedin the circuits as shown.

The effect of the automatic volume control thus applied to the tubes I land i! has the eifect of leveling to a large degree the voltagesdepicted on Fig. 2, which are derived from signals of varying strength.Thus, the voltages shown in the right hand part of Fig. 2 may be derivedfrom a signal having a signal strength at the antenna of the order of ahundred times that of the signal from which the voltages shown on theleft-hand side of Fig. 2 are derived. Thus, the application of automaticvolume control renders the curves 8! very similar and mults in arelatively uniform intermediate frequency s al from all receivedstations, irrupective of very great diif'erences in signal strength. Bythe use of especially powerful A. G. C., such as will be described withreference to Fig. 5, weak and strong stations may be made to producesignals of substantially similar appearance. However, when this is done,the condenser will stop with equal facility on relatively weak andstrong stations alike. Therefore, some difference must be preservedbetween the signals if it is desired to have the condenser stop only onthe stronger carriers. A sensitivity control Ill for adjusting thestop-on-carrier system to stop only at stations of a greater thanpredetermined signal strength is shown in Fig. 1. Moving the adjustablecontact H8 upward causes the condenser to stop on weaker stations, whilemoving the contact H8 downward causes the condenser to stop only onstations giving a more powerful signal.

The operation is as follows:

When the set is inoperative, the relay 45 is de-energized and thearmature 48 is in the position shown in Fig. 1. When the switch 28 isclosed, the motor circuit is complete through the conductor 31, one orthe other of the windings 88 or 86, the switch 42, conductor 43, contact44, and armature 48 to ground. Consequently, the condensers are rotatedin one direction or the other. At the end of their movement, thedirection is reversed, and this condition continues until the tubes warmup to energize the relay 45 with sufficient strength to attract thearmature 48 from its initial position. This occurs when the condenser istuned to a station which will provide a signal of greater strength thana predetermined minimum. If desired, a manually operated or time delayswitch 31" may be included in the conductor 8! to prevent the motor 84from operating until the filaments have warmed up and current flows inthe relay 45. The diode detector elements of the tube l4 will passcurrent in one direction between the cathode and twin plates of thediode, owing to their connection through the resistances I1 and 18, thusestablishing a voltage drop across these resist ances. Consequently, thediode detector i4 supplies to the plate 58 a negative bias. Thisnegative bias is shown graphically for two different stations ofdifferent strength on Fig. 2, being designated by the reference numeral19. On the graph shown in Fig. 2, the position of resonance of theintermediate frequency signal with the natural resonance of the circuitscontaining the windings II and is shown on the abscissa at zero.

To provide high fidelity reception from the loud speaker it, the curve19, which represents the selectivity characteristics of the intermediatefrequency circuits supplying the detector l4, must be fairly broad atthe top. The addition of the winding Ii establishes a mutualinductancebetween this winding and the winding 18. The

result is that the curve 18 tends to have a dual peak, as shown in Fig.2. The depth of the depression between the dual peaks may be regulatedby the degree of coupling between the windings l5 and I3. Closercoupling will accentuate this central depression. The strength of theeffective signal is increased thereby, but too close a coupling willcause distortion.

It will be understood, of course, that the negative bias applied to thegrid 88 which is used as the plate of the diode element in the tube 85,from the diode detector I4, does not cause current to flow in thecircuit containing the diodecathode 58 and the diode plate 59. In orderfor such current to flow, it is necessary to apply a positive voltage tothe plate 58, which is greater than the negative voltage supplied fromthe diode l4. This requisite positive voltage is derived from thewinding 15 which is loosely coupled to the winding 18, and it is showngraphically on Fig. 2, being designated by the reference numeral 88.Owing to the fact that the winding 15 is part of a low loss circuit,loosely coupled to the windings I8 and 14 and tuned to the intermediatefrequency, the curve is quite sharp. It will be understood that thecurve 80 corresponds to the selectivity characteristics of the tunedcircuit containing the winding 15; therefore,the positive portion of theintermediate frequency signal is impressed on the plate 59 in accordancetherewith. This positive voltage is the effective voltage.

In Fig. 2, the curves 82 represent the algebraic sum of the negative andpositive voltages indicated by points on the curves 1! anti 80,respectively, on the same vertical line. It will thus be seen that thecurves 82 represent the voltage effective for causing rectification inthe diode section of the tube 55 to impress a positive bias on the grid60.

Referring to the left hand side of Fig. 2, it will be noticed that up toapproximately two kilocycles on each side of the optimum tuningposition, that is, the position of the condensers corresponding to zeroposition on this graph, there is no possibility of current flowing inthe rectifier circuit connected to the plate 58 and the cathode 56. Thesame is substantially true with the case of a much stronger signal, asshown on the right hand side of Fig. 2. The horizontal line 8| on thisfigure corresponds to the minimum positive voltage necessary to beapplied to the plate 59 to cause rectification to occur and suiiicientcurrent to pass resulting in a suflicient positive voltage being appliedto the grid 68 to cause the armature 44 of the relay 45 to break themotor circuit and stop the rotation of the tuning condenser. It isapparent that this line intersects the two curves 82 at points 83, whichare close to the same distance from the optimum tuning positionindicated by zero. It will thus be seen that the curves of effectivevoltage 82 are made of substantially equal width at the base and offairly similar widths at an operating level indicated by the line 8| bymeans of this invention. The wide sloping base portion of the curve 80is cancelled by the similar portion of the curve 19, thus completelyeliminating this broad, inexact portion of the signal. It thus becomespossible to approach similar widths of signal by reducing the height ofthe operating level 8| by increasing the sensitivity of the relay orvarying thebias on the grid 68.

It may here be pointed out that the sensitivity control H6 functions inthe following manner:

When the slider H8 is moved downwardly, the

. control grid of the tube I I made more negative.

signal of certain weak stations will correspond to a curve 82 which isnot high enough to reach the operating level line 8|. These stationswill then not be tuned in by the stop-on-carrier system. If, on theother hand, the slider H8 is raised to a higher level, the weakerstations will produce curves 82 projecting above the operating levelline 8| and will then cause the relay 48 to stop the condenser on theircarrier waves. Thus. the sensitivity control 8 functions to cause thecondenser to stop or fail to stop on the weaker stations, as desired.

It will readily be seen that the endwise moving parts of the motor 84andthe gang of condensers 22 have a certain inertia which causes thecondensers to continue to move for a brief interval after the motorcircuit is broken. These parts can be readily constructed so that theoverrun brings the condenser substantially to the position of optimumtuning; that is, the position corresponding to the zero line in Fig. 2.When the curve 82 is very narrow, it is desirable to construct thecondenser drive mechanism, the disengaging clutch 8 I' and 32, and therotating parts of the motor 34 so that the condenser will come to a stopas quickly as possible after the opening of the contacts 44. It is alsodesirable under these circumstances that the relay armature 48 be ofsmall inertia and the relay as a whole be constructedior quickoperation.

When the motor is running, that is, when the armature 48 is in theposition shown in Fig. l, the grid 88 is about ground potential. At thesame time, the cathode 51 is at a potential higher than ground, owing tothe drop across the resistors 88 and 88. When, however, a voltagegreater than that corresponding to the line 8I on Fig. 2 is applied tothe plate 58, a current flows in the rectifier circuit, including theoathode 58 and the plate 89, which renders the grid 60 positive to asuillcient degree to induce a plate current through the winding of therelay 48 which is sufllcient to attract the armature 48 and open themotor circuit. As previously explained, the opening of the motor circuitcorresponds to a point such as one of those indicated at 83 on Fig. 2,and the inertia carries the condensers on to a slight extent so thatthey are located very substantially to the optimum tuned positioncorresponding to the zero position on When the relay 48 moves away fromits position shown in Fig. 1. the circuit of the contact 58 is broken,with the result that the grid 88 is made strongly positive, thusensuring the energization of the relay 45 while that station is tunedin, notwithstanding that the signal of the station may fade below thatcorresponding to the line 8| on Fig. 2, or even if the station ceasesbroadcasting entirely.

It .will be noted that when the motor 48 is operating, the grid of thepower tube I is grounded, and consequently the receiver is muted untilthe relay 48 is again energized to withdraw the armature from thecontacts 44, 49 and 88.

terrupting the plate circuit which was energizing the relay 48.Consequently, the spring 8| moves the armature 48 into the positionshown in Fig. 1 and the motor operates as long as the switch II is heldopen. After the-switch II is closed. the motor continues to operateuntil a carrier of suflicient strength to actuate the relay 45 is againreceived, whereupon the receiver will receive that station until the setis turned off or one of the switches II is opened. v

. The embodiment of the invention illustrated in Fig. 3 is intended toexemplify an A. C. set in which an alternating current motor 84 isemployed. The windings of this motor are connected to a contact 88 ofthe relay 88, which is comparable to the relay 48 of the embodimentshown in Fig. 1. One pair of windings of the motor 84 are connected to aconductor 81 which is connected to a leaf 88 of a reversing switch 89.The other pair of windings are connected by a conductor 88 to anotherleaf M of the switch 89. Between the leaves 88 and 8| is a leaf 82 whichis actuated by the armature 98 of a relay 94. The armature 93 is biasedawayi'rom the relay 84 by a spring so that the leaf 92 normally makescontact with the leaf 88. The leaf 92 is connected to one end of thesecondary of a transformer 88, the other end of which is grounded. Theprimary of the transformer 9 is supplied by alternating current from themains, the object of the transformer 98 being to reduce the voltage tosuitable proportions for the operation of a small split phase capacitormotor, such as 84. The armature 93 is also rigidly connected to a leaf91 which is adapted to cooperate with a leaf 98. The leaves 81 and 98are out of contact when the relay 94 is de-energized, and they are incontact when the same is energized.

The two sets of windings of the motor 84, that is, the sets which areconnected to the conductors 81 and 88, respectively, are connectedthrough a capacitor 99. It will readily be understood that when currentis supplied to the lead 81, the motor 84 will rotate in one direction.whereas when current is supplied to the lead 88, the motor will rotatein the opposite direction. Consequently, the direction of rotation ofthe motor depends primarily on the state of energization orde-energization of the relay 94. It may here be noted that in theembodiment of the invention illustrated, the motor 84 tends to rotatethe gang of condensers 22 in the clockwise direction or to theright'when the relay 84 is de-energized. When this relay is energized.the motor tends to operate to the left or in the counterclockwisedirection, as viewed in Fig. 3.

The secondary of the transformer 98 is also connected to the winding ofthe relay 84 and this winding is also connected to a leaf I88. The leafI88 is normally in contact with the shorter leaf III, which is connectedby a conductor I82 to the leaf 81. The conductor I82 is also connectedto a conductor I88, which may be one of three long conductors which maypass through a cable I84. the other two conductors being designated'llland I88. The cable "4 may be of any suitable length and it may beprovided at its end with a remote control unit designated generally bythe reference numeral I81. This remote control unit may comprise anysuitable container having'two leaves I88 and I88, which are normallybiased into engagement with contacts III and II I respectively. The con-H2. The two leaves I03 and I33 are adapted to be actuated by two buttonsH3 and H4 respectively in such a manner that when the buttons are pushedinwardly, the leaves I33 and I03 move away from the contacts III andIII, respectively. When the button H3 is thus depressed, it brings theleaf I03 into engagement with a contact II5. Preferably, the contact IIIis somewhat resilient so that it follows the leaf I03 to a limitedextent, remaining in engagement therewith until the leaf I33 has engagedthe contact H5. The leaf I03 is connected to the conductor I05 and thisconductor is preferably grounded at the set. The contact H5 is connectedto the conductor I03. The leaf I33 is connected to the conductor I05.The conductor I06 is connected to a resistance I35, the opposite end ofwhich is grounded.

The gang of condensers is indicated by the reference numeral 22, as inthe previous embodiment of the invention. The shaft 23 of the gangcarries opposite arms I I1 which carry pins H3 and H3 which areanalogous to the pins 43 and 41 of the embodiment of the invention shownin' Fig. 1. It will be noted that when the condenser rotors move in thecounterclockwise direction, as viewed in Fig. 3, into one extremeposition, the pin H3 engages the long leaf I 00 and sepaq rates it fromthe leaf IOI, thereby breaking the circuit of the relay 34, allowing theleaves 32 and 31 to attain the position shown in Fig. 3 which has, aswill hereinafter be more fully explained, the effect of reversing thedirection of rotation of the motor and causing the condenser shaft 23 toturn in the clockwise direction. When the shaft is thus rotated in theclockwise direction nearly to the full movement of the gang ofcondensers, the pin II3 engages the long leaf I00 and carries thecontacting leaf I 0| into contact with a leaf I20, which is normally outof' engagement with the leaf I M grounded.

The leaf 98 is connected to a contact I2I by a conductor I22. A contactI23 is located adjacent the contacts 35 and I2I so as to be engaged bythe armature I24 of the relay 36 when that relay is disengaged. Thearmature I24 is biased into engagement with these contacts by a springI25. The armature I24 is grounded. The contact I23 is analogous to thecontact 43 of the previously described embodiment and it serves to mutethe set when the armature I24 is in engagement with the contacts 85, I2Iand I23 during the operation of the motor 84.

In this embodiment of the invention, I provide a diode I26, which may beregarded as one of the diodes of a No. 6H6 tube, and a D. C. amplifyingtube I21, which may be a No. 76 tube instead of the diode-triode tube 55of the embodiment shown in Fig. 1. The elements of the tubes are giventhe same numbers as in Fig. 1. The plate 59 of the tube I26 is connectedto the tuned winding 15, which is loosely coupled to the winding 13.This, together with the closely coupled winding 14, constitutes thetransformer 12 between the intermediate frequency tube and diodedetector and first audio tube, as in the previously describedembodiment.

The conductor I22 is connected through a resistor I23 to the cathode 56of the tube I23. This cathode is connected to the grid 30 of the tubeI21 and is by-passed to ground through a condenser I23. The cathode 51of the tube I21 is connected through a resistor I30 to a conduc- Theleaf I20 is tor I 3|, which is connected to the B supply I32 and thewinding of the relay 33. The winding of the relay 36 is also connectedto the plate 54 of the tube I21. The cathode 51 of the tube I21 isconnected to ground through resistors I33, I34, and I35 in series. Theconductor I22 is connected by the resistor I36 to the adjacent ends ofthe resistors I33 and I34. The conductor I33 is connected by a conductorI31 to the common ends of the resistors I34 and I 35.

When the set is inoperative, the relay 34 is deenergized and thearmature 33 is in the position shown in Fig. 3. The armature I24 is inengagement with the contacts 35, I2I and I23. When energy is supplied tothe receiver, which may be done by means of a switch corresponding tothe switch in the previously described embodiment, current is suppliedfrom the transformer 33 through the leaf 32 and leaf 33 to the conductor31, motor coils, contacts 35 and I24 to ground. Consequently, the motoroperates to drive the shaft 23 to the right or in the clockwisedirection, as viewed in Fig. 3. When the pin I I3 is thus brought intoengagement with the leaf I00, the leaf I00 and the leaf IOI are broughtinto conductive relation with the grounded leaf I20. The result is thatthe armature 33 is attracted and current is now supplied to theconductor of themotor 34, thus causing the motor to operate in thereverse direction; that is, to the left. The leaves IN and I20 separateimmediately this reverse direction begins, but the relay. remainsenergized through the leaves I00 and IN, which are connected to groundthrough the conductor I02, leaves 31 and 33, conductor I22, contact I2I,and armature I24. The movement of the gang of condensers to the left isthus maintained until the pin I I3 separates the leaves I00 and IN, thusbreaking the circuit of the relay 34 and allowing the armature 33 toattain the position shown in Fig. 3, which adapts the device forcondenser operation in the clockwise direction. Consequently, the tuningdevice moves from one extreme position to the other until the tubes areheated up sufficiently to bring in a station with suiiicient strength tostop the motor, in substantially the same manner as described inconnection with the embodiment of Fig. 1.

As in the previously described embodiment, no current flows between theplate 53 and the cathode 56 until the plate 53 becomes positive relativeto the cathode 53. When plate current flows through the resistor I23 toground through the contact I2I and armature I24, a certain positivepotential is applied to the grid 30 so that it may become more positive.When a signal which gives a curve 32 (Fig. 2), which is greater than thevoltage corresponding to the line 3|, is received, sufficient currentflows through the relay 36 to energize it and the armature I24 iswithdrawn from the contacts I23, I2I, and 35, and the motor circuit isbroken. When the armature I24 moves away from the contact I2I, B voltageis applied through resistor I30, resistor I33, resistor I36, andresistor I23 to the grid 60, so that a still larger current flowsthrough the relay 33, maintaining this relay energized indefinitely evenif the received signal fades or ceases. The resistor I is preferablyquite large in comparison to the resistors I33 and I34, but is quitesmall compared with the resistor I30. The resistor-I35 is not normallyin the circuit of the cathode 51, since the resistor I34 is groundedthrough conductors I31, I06, 2, and "5, Thi ground circult isinterrupted when either of the two buttons H3 and ill ispressed, withtheresult that the relatively large'resistor I35 is introduced into theplate circuit, reducing the current through the relay 86 to such anextent that the armature I! is released. Itwill be noted that theswitches II in the previously described embodiment open theplatecircuit. In the present embodiment,

'10 this transformer, which is closely coupled tothe the introduction ofthe high resistance III into the plate circuit is distinctly analogousand has the same effect.

When the button H4 is pressed inwardly, it merely has the eifect ofintroducing the resistor E35 into the plate circuit of the tube i2'l.Consequently, the motor will operate towards the right, and if thebutton Ill is held inwardly, the rotor of the condenser 22 will bedriven to the right, until at last the pin 8 comes in contact with theleaf Ill and starts the motor to the leit in the manner previouslydescribed; that is, through the energizatlon of the relay 94. when thisrelay is energized, the button ill, being still pressed inwardly, it islocked in energized relation through leaves III, III, conductor ill,leaves 91 and 98, conductor [22, contact ill, and armature [24. I! thebutton Ill is still maintained pressed, the pin ill breaks the circuitof the relay 84 and movement of the condenser to the right is againresumed. If, at any point of so the cycle thus described, the button Illhad been released. the motor would continue to tunethesetuntilanarresting carrierwastunedin.Thisarrestingcarrierwouldresultinencrgila tion of the relay 8', thestopping of themoior II, and the de-energization of the relay ll, if itwere in a state of energization.

Ashaspreviomlybeenremarkedthe contact I preferably follows the leaf Illwhen the button illispressedinwardlyuntilthe leaf "Ihasengagedthecontact Ill. Whenthebutton H3 is pressed inwardly, therelay is energiaed.the circuit beingas follows: secondaryof transformera, relay, conductor III, conand Ill again brought into contact. Thus,

any'chanceofinjuiytothemotorispreventedbyprovidingforthereversalofthemotorat bothends of the throw of thegangof condensers.

It will be understood. of course, that lithe button 3 is pressedinwardly and then released, the gang of condensers will start moving tothe left and the, motor will be arrested when a carrier wave ofsuflicient strength isbrought in.

Itwillbeunderstood that the contact ill may be stationary so-that themotor can be started to the rightby depressing the button illsufilclently to disengage the pole Ill from the contact III. I! thebutton 3 is further depressed I may be omitted, the conductor. 2 beingconnected directly to the conductor I".

In the embodiment of theinvention shown in Fig. 4, the reference numeralill indicates the lastintermediate frequency tube, the plate of which isconnected to the primary I of a transformer I, which is analogous to thetransformer I! or the previously described embodiments of the invention.The secondary ill of primary I, is connected to the diode plate I42 andthrough resistors M3 and I to the cathode Eli, which is located in thetube Hi with the diode plate I. The tube I also includes the triodeelements, that is, the grid I and the plate I". The grid M! is connectedto the adjacent ends of the resistors I and I. The secondary winding Iand the resistor ill are connected through a resistor m, condenser I58,

and a volume control III to the grid of the first winding I", which isloosely coupled to the transformer I, being analogous to the winding 15of the previously described embodiments.

The winding I53 istuned to the intermediate frequency by the condenserIll. The end of the winding I53 remote from its connection to the plateis connected through a resistor iii to ground and is also connected tothe grid I of the tube H1. The cathode II. of the tube i5! is connectedthrough resistors I59 and I to ground. The common ends of the resistorsI59 and I" are connected by the conductor It! 5 to a contact I82. Aplate I of the tube ii! is connected through the relay I" to the Bsupply "I. The end of the winding of the relay remote from itsconnection to the 3 supply l6! isconnectedthrougharesistor Ill toapole'40 ill of the normally open switch "2. When the pole "I is manuallydepressed, the resistor I'll is grounded. A contact. [1}, which islocated adjacent the contact I82, is connected by a conductor ill to thegrid circuit of the audio fre- 5 quency tube, not shown. A contact I'll,which is located in alignment with the contacts In and "I, is connectedby a conductor III to the motor (not shown). when the relay I" isenergiaed, the armature I" is moved into engage- 5 ment with thecontacts m; m and Hi, thereby mnting the receiver, driving the motor,and increasing the energisation of the relay i". It will thus be seenthat this relay I" is-quite analogoustotherelay 4i oftheiirstdescribedembodiment, but it operates in the opposite direction.

when the button "I is depressed, the motor starts operating, and when acarrier of sufllcient strengthisreceivedtheiiuxoftherelay I decreasesand the armature I" is moved away from it by a spring I'll. The removalof the armature H! from the contact It! decreases still further the fluxof the relay I, thus providing a locking elect. This locking effect can,

however, be obtained in other ways; for example,

the armature i'll'may be arrested by a' stop l'll' sumciently far awayfrom the relay I" so that thecurrentnecessarytoenergizethe'relay illsoastomovethearmamre i'l'l towardsthereesoastobringtheleaflllintoengagementwith 7o lamismuch greaterthanthecurrent strength the contact Hi, the motor will start to the left.Consequently, I may have one button 3 or a plurality of similar buttonsarranged in parallel, each of which can start the motor to the right atwhich therelay Ill releases the armature I" under the action of thespring vI'll. The operation is as iollows;

when energy is supplied ,to the set, the conor the left, as desired. Inthis case, the button denser remains inoperative until the t bes w r up.If the condenser is tuned for the reception of a station of sufllcientstrength, that station will be received. If the switch I" is closed, Bcurrent fiows through the relay coil I55 and resistor I10, and thegrounded relay armature I11 will be brought into engagement with theconiiacts I52, I15 and I15, and the motor will operate as long as thecontact is depressed. It will be understood that the motor may bereversed in the manner described in connection with Fig. 1. If theswitch IN is opened after being pressed momentarily or for a longerperiod, the motor continues to operate until a carrier wave ofsufficient strength is received, which carrier wave has the effect ofdecreasing the plate current of the tube I51, so that the spring I15opens this relay and terminates the operation of the motor.

It will be understood that the cathode I45 and the plate I42 constitutethe second detector of the receiver. This diode circuit creates avoltage drop across the resistors I45 and I44, with the result that thegrid I41 is more negative than the cathode I45. The signal strength isproportional to the drop of potential across the resistor I44, so thatthe stronger the signal, the

greater is the negative voltage applied to the grid I41 relative to thevoltage of the cathode I45. Thus, the stronger the signal, the greateris the tendency for the grid I41 to oppose the passage of plate currentbetween the plate I45 and the cathode I45. The negative voltage appliedto the grid I41 varies in the general manner shown by the curve 15 onFig. 2, it being understood, however, that the curve '15 involves theampliflcation factor of the triode elements I45, I41 and I45, whichconstitute a grid controlled rectifier. The positive component of theloosely coupled winding I53 is applied to the plate I45 and has acharacteristic corresponding to the curve 50 of Fig. 2. Consequently,the plate current, corre-. sponding in magnitude to the curve 52 of Fig.2, will flow between the plate I45 and the cathode I45 when a station ofsufficient magnitude is brought in. This plate current passing throughthe resistor I55 lowers the voltage of the grid I55 so that the platecurrent of the tube I51 is reduced sufficiently to effect the withdrawalof the armature I11 from the contacts I52, I15 and I15 under the actionof the spring I15. It will be understood that the station thus receivedmay fade or sign off without the relay I55 being energized sufficientlyto again attract the armature I11. The reason for this is that thecontact I52 is no longer grounded and has the effect of increasing thepositive bias of the cathode I55, thereby decreasing the current flowingthrough the relay I55, and furthermore, the armature I11'is removed fromthe position of strongest flux of th relay I55.

In the previously described embodiments, a certain negative automaticgain control or A. G. C. voltage' is applied to the grids of certain ofthe earlier tubes of the receiver for the purpose of varying their gainor amplification to secure automatic gain or volume control. Since theresulting reduction of the gain on stronger signals reduces the A. G. C.voltage, the various received signals, while rendered very much moreuniform in strength, still show considerable differencesafter'amplification between the signals produced by a weak and a strongstation. This is exemplified in Fig. 2, where the strength of the signalillustrated on the right is approximately double curves of the left ofthis figure.

I have discovered that I can attain much greater uniformity of signalfor stop-on-carrier tuning by applying the negative A. G. 'C. voltage tothe grid of a radio frequency or intermediate frequency amplifier notlocated in front of the circuit in the amplifier supplying energy to theA. G. C. rectifier. In other words, a more powerful A. G. C. effect canbe obtained from a tube which does not contribute to the amplificationof the signal operating the A. G. C. rectifier. This is true because thereduction of amplification of this tube does not reduce the A. G. C.voltage as is the case when the tube precedes the A. G. C. rectifier. Icall this form of automatic'gain control "after A. G. C." todifferentiate it from the ordinary A. G. C. applied to a tube which isbefore the A. G. C. rectifier and through which the signal operating theA. G. C. rectifier must pass. -By employing both before and -afterautomatic volume control, I may obtain control voltages forstop-on-carrier which are very close to uniformity for all receivedstations. By operating in this manner, I produce a stop-on-carrierreceiver such as that illustrated in Fig. 5, which may cause all thesignals, both weak and strong, which will affect the stop-on-carriersystem, to operate very much alike.

Referring to Fig. 5, the reference numeral I15 designates the lastintermediate frequency tube,

which is coupled'by a transformer I50 to the second detector and firstaudio frequency tube Ill. The detector circuit of the tube I5I includesresistors I52 and I55 from which are derived negative voltages which areapplied by conductors I54 to the grids of certain of th earlier tubes inthe receiver. A conductor I 55 is connected to the two resistors I52 andI55 and to a coil I55 which consists of a few turns tightly coupled tothe primary of the transformer I50. The coil I55 is connected to thegrid of an intermediate frequency amplifying tube I51, which is outsidethe radio receiver circuit. That is, the tube I51 and the tube I55 towhich it is connected through the transformer I55, have no part in theconveyance or amplification of the audible signal. The transformer I55is loosely coupled and its windings are sharply tuned to theintermediate frequency, which has the effect of narrowing the resonancecurve for the signal passing through the tube I51. Consequently, thetube I will onlydraw substantial plate current when the intermediatefrequency signal is near the resonant frequency of the transformer I55.Furthermore, on account of the before and after" A. V. C.,

. the maximum value of the signal of the tube I55 is substantially thesame for all effective stations. The current delivered by the tube I55passes through a relay I50, which controls the motor circuit I5I.

The relay I50 is biased open by a spring I52, and when the relay I50 isopened, its armature I55 makes contact with the motor circuit I5I. Itmay here be noted that the motor circuit may be completed as in themodification of Fig. 1. When the motor circuit is closed, an armatureI55, which is grounded, engages a contact I54 which is connected by aconductor I55 to the grid circuit of the second audio tube, not shown.Consequently, when the motor is operating, the set is mute. When thearmature I 55 is in engagement with the motor circuit I5I and thecontact I54, it opens a switch I55. This switch is arranged to closewhen the relay I50 is energized. One side of the switch I55 is connectedthrough a 5 resistor I51 to the plate of the tube I55 and to one end ofthe winding of the. relay I98. The other end of the winding of th relayI98 is connected to the B supply. The cathode of the tube I88 isconnected through a resistor I98, to the other side of the switch I98.The common point and to the speaker. The automatic volume conof thelatter tube to other audio frequency tubes trol applied by theconductors I84 to the earlier tubes of the receiving set has the eifectof reducing very greatly the difference of strength of signal reachingthe tube 18 I. The after A. G. C. voltage applied by the conductor I85to the tube I81 may be adjusted to render substantially equal signalsappearing in the tube I88 from all stations above a certain signalstrength. Substantial equality may 'be obtained by properlyproportioning the resistors -I82 and I83 to impress the desired portionof the-voltage drop across these resistors on the grid ofthe tube I81.These resistors may also be proportioned so as to get any desired ratioless than equality between the signals produced by the strongest and theweakest stations to be received. It is even possible to make the signalof a strong station produce a smaller signal in the tube I88 than wouldbe produced by a weaker station. It is generally desir-' able toapproach equality between weak and strong stations for the purpose ofvery exact tuning, In addition to the equalizing effect of'40 the afterA. G. C., the loose coupling and sharp resonance of the primary andsecondary circuits of the transformer I89 may be adjusted to make thestop-on-carrier signal highly selective; that is, to narrow the width of.the motor stopping signal in terms of degrees of condenser rotation.

It will be understood that when the plate current of the tube I88 issufllcient; that is, when of suflicient signal strength closelyapproaches the adjusted frequency of the transformer I89, the armatureI93 is moved away from the motor contact and from the contact I94. sothat the motor stops and the station may be audibly received. When therelay: I98 is energized, the.

plate current flows from the B supply through the winding of the relay198, the tube I88, the

resistor I98, and the switch I99. The relay I98 is energized during thereception of a station. The switch I96 is then closed and a parallelcir-' cult is completed from the B supply through the winding of therelay I98, the resistor I81, the switch I98, and the switch I99.Consequently, when the switch I99 is opened, both of these circuits areinterrupted and the relay'I98 is deenergized so that the motor tunes inanother station. -It will be understood that the additional circuit justreferred to has the effect of locking the relay I98 during the receptionof a station until the switch 199 is'opened manually.

The embodiment of the invention illustrated in Fig. 6 comprises a radiofrequency tube 288, an oscillator and first detector tube 28I, a firstintermediate frequency tube 282, a combined diode 283 and secondintermediate frequency elements the intermediate frequency produced by astation 284 enclosed in a single tube 285, a double diode 288, which maybe a No. 61-16 tube, a first audio frequency tube 281, which isconnected to other audio frequency tubes or the loud speaker, and a gastube 288, which may be a No. 884 tube. The last named tube may beconsidered as being out of the set since it is merely used for thecontrol of the relay 289. The set is tuned-by a motor 218 which controlsthe position of three condensers 21I, 212 and 213, which may be arrangedin a gang, as in the first described embodiment of the invention. Thecondensers control a switch 214, which is analogous to the switch 42 ofFig. 1, and which is actuated at extreme positions of the condensertoreverse the motor, tlierebyreversing the direction of movement of thecondenser. The motor 218 is supplied with current from power linesthrough a transformer 215. When the relay289 is de-energized, thearmature 218 is retracted by a spring 211 so as to ground a conductor218 which is connected to the motor 218 through the switch 214 and aconductor, 219, which has the eflect of muting the set v in the mannerdescribed with reference to the previously described embodiments. Whenthe relay 269 is energized, the armature 218 is attracted and breaks themotor and muting circuits.

The plate of the diode 288 is connected through a winding 288, which isgrounded through resistors 281 and 282, which provides a negative A. V.C. voltage. This voltage or part thereof is applied in the before" orafter A. V. C. previously described. Thus, the maximum negative voltageisapplied through a resistor 288 to the grid of the tube 288. A lesserdegree of negative voltage which corresponds to the voltage drop acrossthe resistor 282 is applied through resistor 284 to the grids of tubes28I and 282. A still lesser. amount of the negative voltage, being thatcorresponding to a part of the voltage drop across the resistor 282, isapplied to the grid of the intermediate frequency tube elements 284,this being the position. at which the after'. A. V. C. is applied. Thewinding 288 consists of a few turns closely coupled to the primary of atransformer 288, which connects the plate circult of the tube 282 to thegrid of the intermediate frequency amplifying elements 284 in the tube285. v

For the reasons set forth above, the before and after" A. V. C. gives asignal in the plate circuit of the intermediate frequency elements 264which can be made substantially equal for all received stations, strongor weak. This signal passes through the primary of a closely coupledtransformer 288, the secondary of which is located in the plate circuitof one of the diodes 299 in the tube 288, this secondary being in serieswith a resistor 281. The diode 288 serves as the detector for the set,and the negative side of the resistor 281 is connected through aresistor 289, condenser 298, and volume control 29I to the grid of thefirst audio tube 281. The negative or plate side of the resistor 281 isalso connected through a winding 292-to the plate of the diode 292 inthe tube 288. The cathode of the diode 298 is grounded through aresistor 294. The positive side of the resistor 281 is also grounded.The

ground through a condenser It will readily be understood that the plateoi. the diode 288 is subjected to a negative voltage derived from thevoltage drop across the resistor 281, which voltage drop corresponds toone of the curves 19 in- Fig. 2. The plate of the diode 298 alsoreceives an intermediate frequency signal, the positive phase of whichcorresponds to one oi the curves 88 in Fig. 2. Consequently, the

positive phase of the voltage across the coil 292 impressed upon theplate of the diode 293 is indicated by one of the curves 82 on Fig. 2.It may here be noted that the eifect of the before and "after A. V. C.is to render the two sets of curves shown in Fig. 2 andthe correspondingcurves for both strong and weak stations very much more uniform. Thefurther result is that all of the curves 82 for received stations can bemade practically uniform, both as to height and breadth. As previouslydescribed, it is also possible by applying various portions of thevoltage drop across the resistors 28i and 282 as after A. V. C. toestablish any desired ratio of signal between the strongest and weakestsignals effective on the grid of the tube 288 to be received. Forinstance, the effective signal of the strongest station to be receivedmight cause a voltage change only twice as great as the weakest signalto be received, although the corresponding signals, as received on theantenna of the set, may have a tremendously greater difference.

When a station is being received, current flows in the gas tube 288, therelay 289 is energized, the motor circuit is broken, and the mutecircuit is open. When the switch 388 is opened, the plate circuit of thetube 288 is broken and the armature 218 is released. Consequently, themotor operates until the switch 388 is allowed to close again. After theswitch 388 closes (and it may here be noted that it may be openedmomentarily only), the motor continues to operate until a carrier waveof adequate strength is received, whereupon rectified current fiowsthrough the resistor 298, thereby making the cathode end of the resistor284 positive. This positive voltageis communicated through the resistor298 to the grid of the tube 288. The resistor 298 and condenser 291serve as time filter circuits which prevent the tube 288 from respondingto static or other undesired electrical disturbances of extremely briefduration. It will be noted that the grid of the tube 288 does not needto become positive with respect to the cathode of this tube in order tostart the current through the relay 288. It merely needs to have itsnegative bias reduced below a certain point determined by thecharacteristics of the tube, the plate voltage applied, etc. Thisreduction of negative voltage on the grid of the tube 288 is attainedwhen a received carrier gives a signal corresponding to the curve 82(Fig. 2) of magnitude greater than a certain value, for example, thatcorresponding to the line 8| on this figure.

As has been previously described, the opening of the switch 888 breaksthe plate circuit of the tube 288, resulting in starting the motor 218.

tor continues to operate until the next station of suiilcient strengthis tuned in.-

Itwill be understood that the tube as: passes its full plate current assoon as the negative voltage of its grid falls below the value whichprevents ionization. In other words, the grid acts as a triggercontrolling the plate current, but once ionization is established andplate current flows, the plate circuit must be interrupted, the platevoltage reduced below the ionization point,

orthe negative bias on the grid enormously in- Alter the switch 388 isallowed to close, the mocreased to stop the fiow of plate current. Thisquality of the gas tube therefore provides similar lockingcharacteristics to those obtained in the other embodiments by speciallocking circuits. The action 01 the gas tube 288 is very rapid. Its timecharacteristics, however, can be controlled by means of the timeconstant of the filter circuit composed of the resistor 298 andcondenser 291. Increasing the resistance of the resistors and thecapacity of the condensers increases the time interval, and vice versa.The time filter circuit connected to the grid of the tube 288 should beso proportioned that the action of the tube 288 is as rapid as possible,but still slow enough so as to require a signal of appreciable durationto cause it to ionize. In other words, it should work as rapidly aspossible on a continuous carrier wave, but should not respond to staticor other undesired disturbances of negligible duration.

There are certain considerations pertaining to the time interval betweenthe instant at which the signal is tuned closely enough to resonance toeffect the interruption of the motor circuit and the instant that thecondenser comes to a full stop, which should be considered for properoperation of this invention. Lag or delay tending to prolong thisinterval can occur in several ways. First, the filters employed inconnection with rectifiers contributing to the stop-on-carrier signalmust not have too long a time constant if the quickest possible stoppageis desired. Of course, the characteristics of the whole system must beconsidered. If a sharp selective stopon-carrier signal is employed, thenthe distance or time available between the effective stop-oncarriersignal and arrival at the peak of the carrier wave is very short and thetime constants of all portions of the system must be" made very small toprevent passing the peak of the carrier before complete condenserstoppage occurs. On the other hand, if the stop-on-carrier signal isrelatively broad, then too quick action will result in condenserstoppage before the peak of the carrier is reached. Accuracy anduniformity of tuning are, however, facilitated by sharp tuning of thecarrier signal and corresponding reduction in the time lag all along theline. This procedure in connection with the equalization of theefi'ective width of strong and weak signals is the preferredarrangement.

When the time constants oi the rectifiers are sufliciently short, thenext point of delay to be considered is the stop-on-carrier relay. Theoperation of the relay may be accelerated by reducing the inertia of themoving parts, by reducing hysteresis and eddy current eifects, and bysupplying a large sudden increase of plate current to provide a powerfulrelay action. It is also generally desirable to close the magneticcircuit of the relay for quickest action rather than to open it. Thismeans that fast action is obtained when energization of the relay stopsthe motor. It will be understood that it is desirable also to reduce'permeability or reluctance.

the weight and inertia of the parts rotating with the rotor of thecondenser.- A considerable 1nertia, however, is unavoidable in thearmature or rotor of the motor employed in driving the condenser. It istherefore preferable to provide means whereby the condenser or othervariable reactance can be brought to a full stop while the armature ofthe motor is still rotating. If a clutch is provided for this purpose,as shown in Fig. 1, it is desirable to reduce as faras possible the timerequired for the clutch to release. Other means of eliminating theeffect of the motor armature inertia may also be employed, such as afriction drive between the motor and the condenser with provision forabruptly stopp n the condenser, while the armature may continue torotate for a short interval by slippage of the friction drive.

It will be further understood that the importance of eliminating thestopping lag increases with the speed at which the motor turns thecondenser. If this speed is quite slow, requiring for instance, ten ortwenty seconds for a half revolution of the condenser rotor, the timelag may not need to be especially reduced. It might even be necessary toincrease it. Butit is desirable to drive the condenser at relativelyhigh speed so that only a brief interval is required to tune from onestation to the next. This facilitates selecting the desired station bytuning from one station to the next in the shortest period of time. Itis thought desirable for this purpose to turn the condenser one-halfrevolution in from two to not over five seconds, and it is desirable towork closer to the lower figure.

To achieve the most rapid operation with exactand uniform tuning, it isdesirable that a given number of degrees of condenser rotation shouldresult in changing the tuning by a given number of kilocycles alike fromthe high to the low frequency ends of the tuning range. For thispurpose, a condenser having a substantially straight line frequencycharacteristic, at least to within a short distance of the low frequencyend, may be employed. To keep the straight line frequency characteristicall the way to the low frequency end might involve too great astructural disadvantage in the condenser, although it isdesirableotherwise. A variable inductance may also be employed for tuning, forinstance, one in which the inductance is changed by va y g the In thiscase, a uniform change of frequency with rotation is of similaradvantage. 'With slower tuning, this straight line frequencycharacteristic is of lesser importance.

Although the invention has been described in ing a power actuated tuningelement, a grid controlled gas tube having a cathode and plate, meansfor supplying a steady direct current voltage to the plate of the gastube, fast acting direct current means in the plate circuit of said tubeactuated by' a change in the direct plate current of said gas tube tostop the movement of said tuning element substantially at resonance,rectifying means and means for impressing a voltage from said rectifieron the gridof said gas tube to stop said tuning element.

2. In combination with. a radio device having an adjustable control,electric power means for driving said control in both directions, asource of electric current therefor, relay means for stopping andstarting said power means, a second relay means for reversing said powermeans biased to normally operate said power means in one direction,switch means for energizing said step and start relay means, switchmeans for energizing said reversing relay means, and means for manuallyoperating one switch means to start in one direction and both saidswitch means to start in the other direction. 7

3. In combination with a radio receiver, a tuning element, meansactuated by a change in the plate current of a grid controlled electrontube to stop the movement of said tuning ele ment substantially atresonance, electric power means for driving said tuning element, asource of electric current therefor, relay means for stopping andstarting said power means, a second relay means for reversing said powermeans biased to normally operate said power means in one direction,switch means for energizing said stop and start relay means, switchmeans for energizing said reversing relay means, and means for manuallyoperating one switch means to start in one direction'and'both saidswitch means to start in the other direction.

4. In combination, in a superheterodyne radio receiver having anintermediate frequency section and a second detector, a shieldingcontainer, second detector coupling means within said container, a poweractuated tuning element, a

grid-controlled electron tube, means actuated by a change in the platecurrent of said electron tube to stop said tuning element when theintermediate frequency signal is in substantial resonance with saidintermediate frequency section, means including a pair of circuits tunedto the intermediate frequency housed within said container and havingmutual coupling adapted to produce a first control voltage having aselectivity curve with two peaks and a depression therebetween, meansfor deriving from said receiver a second control voltage having a singlepeak coinciding with said depression and exceeding said first controlvoltage when a carrier signal is closely tuned in, and means includingrectifying means for applying a voltage depending upon the diflerencebetween said first and second control voltages to said electron tubeadapted to produce a change in the plate current .of the electron tube.

5. In a radio receiver, in combination, a variable tuning element, amotor for operating said tuning element, a clutch connecting said motorto said tuning element, an ionizing gas tube having a grid and plate,electrical means in the plate circuit of said gas tube for controllingsaid clutch, tuned coupling means deriving from said receiver a firstcontrol voltage having a seiec-- tivity curve with two peaks and adepression therebetween, tuned coupling means deriving from saidreceiver a second control voltage having a selectivity curve with asingle peak coinciding in frequency with said depression and exceedingfirst said control voltage when a carrier signal is closely tuned in,means including rectifying means for applying a voltage depending uponthe difference between said first and second control voltages to saidgrid to ionize said tube when a carrier signal is closely tuned,thereammo by to cause said electrical means to disengage said clutch andstop said tuning means closely on said carrier signal.

6. In a radio receiver having a variable tuning element, in combination,power means for driving said tuning element, relay means controllingsaid power means and tuning element, said relay means being operablewhen deenergized to render said power means effective to drive thetuning element and when energized to stop said power means and tuningelement, an ionizable gas tubehaving an output circuit connected to saidrelay means and a control grid, means connected to said grid to supplyit with a control voltage from the receiver for ionizing said tube andenergizing said relay when a carrier signal is closely tuned in, asource of direct current connected to said plate circuit for maintainingsaid tube ionized and said relay means energized, and normally closedswitch means in said plate circuit operable to open said plate circuitfor deionizing said gas tube and deenergizing said relay'means.

7. In a superheterodyne receiver having variable tuning means, incombination, a motor for actuating said tuning means, switch meanscontrollable by an operator for starting said motor, an intermediatefrequency transformer having a primary winding tuned to intermediatefrequency, a tuned circuit coupled to the primary of said intermediatefrequency transformer, said circuit being tuned to intermediatefrequency and having a degree of mutual coupling to the primary of saidtransformer such that the selectivity curve of the primary has two peakswith a depression therebetween and the selectivity curve of said tunedcircuit has a single peak coinciding in frequency with said depressionand the voltage of said tuned circuit exceeding that of said primaryonly when a carrier signal is closely tuned in, a rectifier having aplate and a cathode, one terminal of said tuned circuit being connectedto supply said plate with an intermediate frequency voltage, otherrectifying means energized from the primary of the intermediatefrequency transformer and delivering a negative rectified voltage tosaid plate, a tube having a grid and plate with its grid connected tosaid cathode, and a relay operated by the plate current of said lasttube for stopping the motor and movement of said tuning means when thepositive phase of th intermediate frequency voltage exceeds the negativevoltage by a definite amount.

8. In a radio receiver having a variable tuning element, in combination,power means for driving said tuning element, relay means adapted whenenergized to stop said power means and tuning element, an ionizable gastube having a plate circuit connected to said relay means and a controlgrid, means connected to said grid to supply it with a control voltagefrom the receiver for ionizing said gas tube and energizing said relaymeans when a carrier signal is closely tuned in, a source of directcurrent connected to the plate circuit of said tube for maintaining saidtube ionized and said relay means energized, and a time delay circuitconnected between said grid and control voltage source having a timeconstant short as compared to the time of operation of said relay andlong as compared to the duration of static impulses.

9. In a radio receiver having variable tuning means, in combination,electrically actuated means for stopping and starting said timing means,an electron tube having a plate circuit v connected to said electricallyactuated means and a grid controlling the plate current for operatingsaid electrically actuated means, means including a pair of circuitstuned to the same frequency associated with said receiver and having amutual coupling adapted to produce a first control voltage having aselectivity curve with two peaks and a depression therebetween, meansfor deriving from said receiver a second control voltage having a singlepeak coinciding with said depression and exceeding said first controlvoltage when a carrier signal is closely tuned in, means includingrectifying means for applying a voltage depending upon the differencebetween said first and second control voltages to said grid when saidcarrier signal is closely tuned to operate said electrically actuatedmeans and stop said tuning means closely on said carrier signal, andmeans actuable by an operator to operate said electrically actuatedmeans to restart said tuning means.

10. In a radio receiver having power actuated tuning means, incombination, a transformer having a tuned primary circuit and a tunedsecondary circuit coupled thereto to cause the voltage selectivity curveof said primary to have two peaks and to cause the voltage selectivitycurve of said secondary to have a single sharp peak located with respectto frequency at the depression between the two peaks of the primaryselectivity curve and exceeding the voltage of the double peakedselectivity curve when a station is closely tuned in, a thermionic tubehaving a grid and controlling said power actuated tuning means, andmeans including rectifying means for applying a control voltagedependent on the difference between the single peaked and double peakedvoltages to the grid of said thermionic tube to stop said tuning meanswhen a station is closely tuned in thereby.

11. In a radio receiver having variable tuning means, in combination,power means driving said tuning means, relay means for stopping andstarting said power and tuning means, an electron tube having a platecircuit connected to said relay means and a grid for controlling saidplate current for operating said relay means to stop said tuning means,tuned coupling means deriving from said receiver a first control voltagehaving a selectivity curve with two peaks and a depression therebetween,tuned coupling means deriving from said receiver a second controlvoltage having a selectivity curve with a single peak coinciding infrequency with said depression and exceeding said first control voltagewhen a carrier signal is closely tuned, means including rectifying meansfor applying a control voltage depending upon the difference betweensaid first and second control voltages to said grid when said carriersignal is closely tuned to operate said relay means and stop said tuningmeans closely on said carrier signal, means including a circuitcontrolled by said relay upon operation thereof to stop said tuningmeans for applying additional grid bias voltage to said grid to preventa decrease in carrier signal strength from operating said relay means,and means actuable by an operator for operating said relay means torestart said power and tuning means.

12. In a radio receiver having a variable tuning element, incombination, power means fordriving said tuning element, relay meansadapted when energized to stop said power means and tuning element, anionizable gas tube having a plate circuit connected to said relay meansand a control grid, means connected to said grid to supply it with acontrol voltage from the receiver for ionizing said gas tube andenergizing said relay means when a carrier signal is closely tuned in,and a source of direct current connected to the plate circuit of saidtube for maintaining said tube ionized and said relay means energized.

13. In a radio receiver having variable tuning means, in combination,power means driving said tuning means, relay means for stopping andstarting said power and tuning means, an electron tube having a platecircuit connected to said relay means and a grid controlling the platecurrent for operating said relay means to stop said tuning means, tunedcoupling means deriving from said receiver a first control voltagehaving a selectivity curve with two peaks and a depression therebetween,tuned coupling means deriving from said receiver a second controlvoltage having a selectivity curve with a single peak coinciding infrequency with saiddepression and exceeding said first control voltagewhen a carrier signal is closely tuned,vmeans including rectifying meansfor applying a voltage depending upon the diife'rence between said firstand second control voltages to said grid when said carrier signal isclosely tuned to operate said relay means and stop said tuning meansclosely on said carrier signal, and means actuable by an operator foroperating said relay means to restart said power and tuning means.

14. In a superheterodyne radio receiver having an intermediatefrequencysection and variable tuning means, in combination, power means drivingsaid tuning means, relay means for stopping and-starting said powermeans, an electron tube having a plate circuit connected to said relaymeans and a grid controlling the plate current for operating said relaymeans to stop said tuning means, means coupled to said intermediatefrequency section and tuned to intermediate frequency for deriving fromsaid receiver a first control voltage having a selectivity curve withtwo peaks and a depression therebetween, means coupled to saidintermediate frequency section and tuned to intermediate frequency forderiving from said receiver a second control voltage having aselectivity curve with a single peak coinciding in frequency with saiddepression and exceeding said first control voltage when a carriersignal is closely tuned, means including rectifying means for applying avoltage debeing energizable to stop and deenergizable to start saidpower means, an ionizable gas tube having a plate circuit connected tosaid relay means, said tube being non-conductive during operation ofsaid tuning means and having a control grid adapted to be supplied witha control voltage to render said tube conductive to energize said relaymeans, means coupled to said intermediate frequency section and tuned tointermediate frequency for deriving from said receiver a first controlvoltage having a selectivity curve with two peaks and a depressiontherebetween, means coupled to said, intermediate frequency section andtuned to intermediate frequency for deriving from said receiver a secondcontrol voltage having .a selectivity curve with a single peakcoinciding in frequency with said depression and exceeding said firstcontrol voltage when a carrier signal is closely tuned, means includingrectifying means for applying a control voltage depending upon thedifference between said first and second control voltages to said gridwhen said carrier signal is closely tuned to render said tube conductiveand energizesaid relay means to stop said tuning means closely on saidcarrier signal, and means actuable by an operator for deionizing saidtube and deenergizing said relay means to restart said power and tuningmeans.

16. In a superheterodyne receiver having an intermediate frequencysection, an amplifying tube preceding said section, and variable tuningmeans, in combination, power means driving said tuning means, relaymeans for stopping and starting said power means, an electron tubehaving a plate circuit connected to said relay means and a gridcontrolling the plate current for operating said relay means to stopsaid tuning means, means coupled to said intermediate frequency sectionand tuned to intermediate frequency for deriving from said receiver afirst control voltage having a selectivity curve with two peaks and adepression therebetween, means coupled to said intermediate frequencysection and tuned to intermediate frequency for deriving from saidreceiver a second control voltage having a selectivity curve with asingle peak coinciding in frequency with said depression and exceedingsaid first control voltage when a carrier signal is closely tuned, meansincluding rectifying means for applying a control voltage depending uponthe difference between said first and second control voltages to saidgrid when said carrier signal is closely tuned to operate said relaymeans and stop said tuning means closely on said carrier signal, meanscontrolling the grid bias of said amplifying tube for preventingoperation of said relay in response to carrier signals below intensitiesdetermined by said grid bias controlling means, and means actuable by anoperator for operating said relay means to restart said power and tuningmeans.

17. In a radio receiver having a variable tuning element, incombination, power means for driving said tuning element, relay meanscontrolling said power means and tuning element, said relay means beingoperable when deenergized to render said power means effective to drivethe tuning element and when energized to stop said power means andtuning element, an ionizable gas tube having a cathode, plate andcontrol grid, a source of direct current voltage, said source beingconnected across the plate and cathode of said tube in series with saidrelay means, means including a grid bias resistor connected between saidcathode and the negative side of said voltage source and a secondresistor connected between the positive side of said voltage source andsaid cathode for biasing said control grid to deionize said tubewhensaid means is deenergized, and means connected to 18. In a radioreceiver having a variable tuning element, in combination, power meansfor driving said tuning element, relay means controlling said powermeans and tuning element, said relay means being operable whendeenergized to render said power means eifective to drive the tuningelement and when energized to stop said power means and tuning element,an ionizable gas tube having a cathode, plate and control grid, a sourceof direct current voltage, said source being connected across the plateand cathode of said tube in series with said relay means, meansincluding a grid bias resistor connected between said cathode and thenegative side of said voltage source and a second resistor connectedbetween the positive side -of said voltage source and said cathode forbiasing said control grid todeionize said tube when said relay means isdeenergized, means connected to said grid to supply it with a controlvoltage from the receiver for ionizing said tube and energizing saidrelay when a carrier signal is closely tuned in, and normally closedswitch means in the plate-cathode circuit of said tube for deionizingsaid tube and deenergizing said relay means.

'19. In a radio receiver having variable tuning means operable betweenpredetermined limits, in combination, a reversible electric motor fordriving said tuning means in opposite directions, a source of power forsaid motor, means including a relay and switch means operated therebycontrolling the connections of the motor to said power source forstarting and stopping said power means, means including limit switchmechanism actuated by said tuning means and controlling the connections01' said motor to said power source for automatically reversing themotor at the limits of movement of said tuning means, means including anelectron tube having its plate circuit connectedto said relay foroperating said relay to effect disconnection of said motor from saidpower source when a carrier signal is tuned in, and switch meansoperable by an operator controlling said relay and connections of themotor to said power source for reversing said motor when said tuningmeans is between the limits of its movement.

20. In a radio receiver having variable tuning means, .operable betweenpredetermined limits, in combination, a reversible electric motor fordriving said tuning means in opposite directions, a source of power forsaid motor, means including a relay and switch means operated therebycontrolling the connections of the motor to said power source forstarting and stopping said power means, means including a reversingswitch controlling the connections of said motor to said power source, asecond relay controlling said reversing switch and limit switchmechanism actuated by said tuning means adapted to energize said relayat one limit and to deenergize said relay at the other limit of movementof said tuning means for automatically reversing said motor, meansincluding an electron tube having its plate circuit connected to saidfirst relay for operating said relay to eflect disconnection of saidmotor from said power source when a carrier signal is tuned in, andswitch means operable by an operator for energizing said second relayindependently of said limit switch mechanism for initiating operation ofsaid motor in a direction opposite to that determined by said limitswitch mechanism. EDWARD ,1". ANDREWS.

